package src;
import java.util.HashMap;
/**
 * Created by dell on 2017/7/27.
 */
public class HashMapTest {
    public static void main(String[] args) {
        HashMap hm=new HashMap();

        hm.put(1,null);
        hm.put(null,null);
        hm.put(null,"3");


        hm.put("2","3");
        //hm.replace(null,1);
        hm.put("a",1);
        System.out.println(hm);
    }
}
